thanks it is working. Never heard of shape keys (i'm a newby).
There's only one problem left.
The plan is to first add some shape keys for tiny waves (choppy water) and then other keyframes for bigger waves (swell). So the swell (wich is made in sculpt mode) has to move forward while the tiny waves have to stay at their places.
The problem is making a smooth animation of the swell going forward!

the swell is basically a stroke of the F draw in sculpt mode. It is important that the waves aren't separated from the choppy water (plane) because the influence of the chops on the waves are more realistic that way.